Trilobites are an extinct group of arthropods that first appeared early in
the Cambrian Period, and met their demise at the end of the Permian Period.
They occupied a remarkable range of ecological niches of the early Earth's
oceans, and were a prominent part of marine communities for millions of
years. Trilobites were stunningly complex and beautiful animals, which is
why their fossilized remains are extremely sought-after by serious fossil
collectors. And due to their unique anatomy and bizarre body designs,
trilobites are also admired by untrained amateurs. Fossil trilobites have
been found in Native American excavations - they were drilled and used in
ritualistic jewelry hundreds of years ago. These fascinating fossils are
found worldwide, and are important as index fossils, particularly in
Lower Paleozoic rocks. But their appeal extends well beyond scientific
study - one look at these enigmatic critters and you'll know what all the
fuss is about!

ANATOMY

The body of the trilobite was covered by a calcareous exoskeleton which,
as a rule, is divided lengthwise into three "lobes", hence the name
"trilobite." The front part of the dorsal shield is the head, or
cephalon. The middle, lobed, segmented portion, is the body, or thorax,
and the tail section is termed the pygidium. Trilobites were capable of
molting this exoskelton during growth. Usually only pieces of the
exoskelton are found preserved as fossils. But, occasionally, a
trilobite was buried "alive" by sediment, and the entire "shell'' of the
trilobite was preserved fully intact. Most of these ancient arthropods
also had the ability to enroll in times of danger, much
like the present-day "sow bug." When enrolled, the entire soft,
underside of the trilobite was totally protected by the exoskeleton. It
is not that unusual to find enrolled trilobites in the fossil record. In
fact, in some areas, enrolled trilobites are more common than
outstretched specimens.

Trilobites had remarkably sophisticated eyes for ancient, "primitive"
creatures. Although some trilobites were blind, many had large, compound eyes, much like modern insects, with hundreds of individual lenses. Beneath
each body segment was a pair of two-branched legs. One of the leg branches was used for locomotion, while the other leg branch held gills for breathing. Trilobites were filter feeders, detritus eaters, scavengers, or predators. Their mouth was on the underneath side of the cephalon, which led to a straight gut that ended with an anal opening near the end of the pygidium. The mouth was covered with a hard plate, the hypostome, which is one of the few hard parts of the underside of the trilobite. Extending from the front of the trilobite were paired antennae. Fossilized examples of these soft parts of the trilobite (legs, gills, antennae, etc.), are extremely rare and have been found in only a few places in the world.

Trilobites eventually developed a wide range of size, shape, design, and
ornamentation. Although some adult trilobites could fit on the head of a
pin, others attained a size of almost thirty inches long. Some trilobites were very sleek with smooth exoskeletons adapted for scurrying across the sea floor or swimming. Some developed complex, spiny ornamentation, probably as protection against predators. Trilobite diversity reached its peak during Ordovician times. By the beginning of the Mississippian Period, trilobites were no longer prominent, and reduced to rather small, simple designs. Despite all these changes and adaptations, trilobites did not stray far away from their original body plan during millions of years of evolution.

FACTOIDS

There is more to the fossil record of trilobites than their
well-preserved exoskeletons. Tracks and trails of trilobites have long
been recognized as trace fossils. Trilobite trails indicate that these
animals moved in a number of different ways, and burrowed as well. Also,
pits have been found in certain sedimentary rocks that seem to indicate
trilobite resting places. Some species of trilobites were incredibly gregarious, having been found in groups of dozens and even hundreds. These extinct arthropods have even been found fossilized with healed bite marks,
proving that they were prey for larger predators. Trilobites are
favorites of fossil collectors everywhere due to their unique design and
varied forms of preservation. Dinosaurs and trilobites are probably the
two most collected types of fossils in the world. Certain well-prepared
trilobites are literally worth their weight in gold. In the hands of a
skilled preparator, a simple "bug in a rock" can be transformed into an
ancient life sculpture - a natural Work of Art, if you will. Hopefully, these fascinating creatures will continue to amaze and inspire scientists and collectors alike for many generations to come.